1. Field of the Invention
The present invention relates to a balance shaft module, and more particularly, to a low noise type balance shaft module with noise of a sub-oil pump reduced.
2. Description of Related Art
In general, balance shaft modules are an assembly of a balance shaft and an oil pump, which is modulated and fastened to the lower portion of a cylinder block.
The balance shaft attenuates secondary non-uniform force generated reciprocating masses, such as the pistons and a connecting rod of an in-line four cylinder engine and also attenuates secondary vibration due to the secondary non-uniform force, such that it improves acceleration booming.
The balance shaft module is equipped with a dual oil pump including a main oil pump and a sub-oil pump to satisfy lubrication performance of the engine.
The dual oil pump sucks the engine oil from an oil fan in the idle state of the engine, using the main oil pump and the sub-oil pump, and a flow control valve that is opened by pressure of the sucked oil determines the flow rate of the oil discharged to the engine.
Since high engine performance requires higher lubrication performance, the dual oil pump also requires increase of the capacity, but the layout of the main oil pump is limited by the increase of capacity, such that increasing the capacity is not easy.
The sub-oil pump of which the layout is not limited, different from the main oil pump, can use the increase of by-pass pressure due to the increase of pump rotor width and opening pressure. Therefore, it is possible to easily increase the capacity of the dual oil pump by increasing the capacity of the sub-oil pump.
The sub-oil pump re-circulates the oil in the transition section above 7000 RPM and the amount of the oil discharged to the engine due to the increase of capacity is little increased, but it is possible to increase the amount of oil discharged to the engine in the substantial operation section (idle˜less than 7000 RPM).
Therefore, it is possible to satisfy the requirement for increasing lubrication performance of the engine having increased performance, in the dual pump equipped with the sub-oil pump having increased capacity.
However, the increase of the oil pump capacity generally increases noise, such that the same phenomenon necessarily occurs in the sub-oil pump.
That is, the increase of capacity of the sub-oil pump increases the pump rotor's moment for pumping the oil and the increase of the pump rotor's moment increases the discharge pulse pressure more increasing the whine noise, and as a result, the whine noise necessarily increases in the sub-oil pump having increased capacity.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.